1. Field of the Invention
The present invention relates to a method for producing ortho-alkylated phenols.
2. Description of the Related Art
Aromatic ring alkylated phenols are industrially used as raw materials or intermediates of medical and agricultural chemicals, resins, various additives, polymerization inhibitors, antioxidants, disinfectants, preservatives, industrial chemicals and the like. For example, thymol having a structure in which an isopropyl group is bonded to 2-position and a methyl group is bonded to 5-position of phenol is used as a vermicide.
Conventionally, for producing ortho-alkylated phenols, a gas phase reaction in which phenols and alcohol are vaporized and allowed to flow through a catalyst phase for reaction, a liquid phase reaction utilizing a Friedel and Crafts"" reaction, and other methods, are known. JP-A No. 2000-38363 discloses a method in which phenols and alcohol are heated at 400xc2x0 C. in the supercritical region using zirconium oxide as a catalyst to produce ortho-alkylated phenols. However, this method has a problem that when the reaction is conducted by a batch system, components having higher boiling points composed of dimers of phenols and derivatives thereof as main components are by-produced in large amount.
An object of the present invention is to provide a method for producing ortho-alkylated phenols from phenols and alcohol, with high selectivity and by-producing a small amount of components having higher boiling points even if the reaction is conducted by a batch system.
The present inventors have intensively studied a method for producing ortho-alkylated phenols by a reaction of phenols with alcohol, and resultantly found that ortho-alkylated phenols can be produced, by reacting phenols with alcohol using germanium oxide as a catalyst under the supercritical condition of the alcohol or by reacting phenols with alcohol in the presence of germanium oxide and carbon dioxide under conditions in which a mixture of alcohol and carbon dioxide is in the supercritical condition, with high selectivity and by-produced a small amount of components having higher boiling points even if the reaction is conducted by a batch system, and have completed the present invention.
Namely, the present invention relates to [I] a method for producing ortho-alkylated phenols comprising reacting phenols represented by the general formula (1) with monohydric or dihydric alcohol in the presence of germanium oxide under conditions in which said alcohol is in the supercritical condition, wherein each of R1, R2, R3, R4 and R5 independently represents a hydrogen atom, or a linear or branched alkyl group having 1 to 10 carbon atoms. 
Further, the present invention relates to [II] the method according to [I], wherein the method comprises reacting phenols represented by the general formula (1) with monohydric or dihydric alcohol in the presence of germanium oxide and carbon dioxide under conditions in which a mixture of said alcohol and carbon dioxide is in the supercritical condition.
The present invention will be illustrated in detail below.
As the linear or branched alkyl group having 1 to 10 carbon atoms represented by R1, R2, R3, R4 and R5 in phenols of the general formula (1) used as a starting raw material in the present invention, amethyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group and the like are listed, and as specific examples of phenols of the general formula (1), phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 3,4-xylenol, 3,5-xylenol, anisole, t-butylphenol and the like are listed.
In the present invention, the alcohol which is another starting raw material is not particularly restricted providing it is monohydric or dihydric alcohol, and it is preferably monohydric alcohol of the general formula (2):
R6xe2x80x94OHxe2x80x83xe2x80x83(2)
(wherein, R6 represents a linear or branched alkyl group having 1 to 10 carbon atoms). Here, a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group and the like are listed as R6.
As themonohydric alcohol of the general formula (2), methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, n-octanol, n-nonanol, n-decanol and the like are specifically listed, and because of high selectivity, methanol, ethanol, n-propanol and n-butanol are preferable, methanol and ethanol are more preferable, methanol is further preferable.
As the dihydric alcohol, ethylene glycol, propylene glycol and the like are listed.
In the present invention, the molar ratio of monohydric or dihydric alcohol to phenols of the general formula (1) is appropriately determined depending on compounds used, and generally from 1 to 1000, and ratios from 1 to 200 are preferably used.
Substances have inherent three conditions, gas, liquid and solid, and further, at the critical temperature or more and critical pressure or more, a fluid phase exists which is not condensed even if it is pressed. This condition is called the supercritical condition.
When a substance is chemically reacted in fluid under the supercritical condition, this substance may manifest higher reactivity than in fluid under gas phase condition and in fluid under liquid phase condition, the reason for this being not apparent, and being guessed that the fluid under the supercritical condition presumably has high density and high diffusion property.
Further, under the supercritical condition, the size of a reaction apparatus can be decreased as compared with the gas phase reaction since the supercritical condition has a density near liquid phase.
In the present invention, the upper limit of the reaction temperature is not restricted, and preferably 450xc2x0 C. or less so that phenols of the general formula (1) are not decomposed. The upper limit of the reaction pressure also is not restrictive, and preferably 25 MPa or less since it is expensive to increase pressure resistance of a reaction apparatus.
In the production method [I] of the present invention, a reaction is conducted under conditions in which monohydric or dihydric alcohol is in the supercritical condition in the presence of germanium oxide. When methanol is used as this alcohol, the reaction is conducted under conditions of 240xc2x0 C. or more and8MPa or more since methanol has a critical temperature of 240xc2x0 C. and a critical pressure of 8 MPa. When ethanol is used, the reaction is conducted under conditions of 243xc2x0 C. or more and 6.3 MPa or more since ethanol has a critical temperature of 243xc2x0 C. and a critical pressure of 6.3 MPa. When n-propanol is used, the reaction is conducted under conditions of 264xc2x0 C. or more and 5 MPa or more since n-propanol has a critical temperature of 264xc2x0 C. and a critical pressure of 5 MPa. When isopropanol is used, the reaction is conducted under conditions of 235xc2x0 C. or more and 4.8 MPa or more since isopropanol has a critical temperature of 235xc2x0 C. and a critical pressure of 4.8 MPa. When n-butanol is used, the reaction is conducted under conditions of287xc2x0 C. or more and 4.8 MPa or more since n-butanol has a critical temperature of 287xc2x0 C. and a critical pressure of 4.8 MPa.
Next, the production method [II] of the present invention will be illustrated.
In the production method [II] of the present invention, a reaction is conducted in the presence of germanium oxide and carbon dioxide under conditions in which a mixture of monohydric or dihydric alcohol and carbon dioxide is in the supercritical condition.
The mixing ratio of the above-mentioned alcohol to carbon dioxide is not particularly restricted, and determined in view of the solubility of phenols of the general formula (1) used in the reaction into the above-mentioned alcohol. The mixing ratio of the above-mentioned alcohol to carbon dioxide is preferably from 10:90 to 99:1.
A case in which methanol is used as the above-mentioned alcohol and phenol is used as the phenols of the general formula (1) will be specifically illustrated. For example, in the case of a mixture having a molar ratio of methanol to carbon dioxide of 75:25, this mixture has a critical temperature of 204xc2x0 C. and a critical pressure of 12.75 MPa according to J. Chem. Thermodynamics, vol. 23, p. 970 (1991).
When ortho-methylation of phenols is conducted under temperature and pressure conditions in which a mixture of methanol and carbon dioxide is in the supercritical condition, temperature and pressure conditions are necessary under which the mixture is in the supercritical condition. For example, in the case of the above-mentioned mixture having a molar ratio of methanol to carbon dioxide of 75:25, it is necessary to conduct the reaction at a temperature of 204xc2x0 C. or more and a pressure of 12.75 MPa or more, and the reaction is preferably conducted at a temperature of 240xc2x0 C. or more and a pressure of 12.75 MPa or more.
The reaction times in the production method [I] of the present invention and the production method [II] of the present invention are appropriately determined depending on the kinds of the phenols and the alcohol, respectively, and the like, and usually in the range from 1 minute to 24 hours.
In the respective production methods of the present invention, it is preferable to effect a batch system reaction of phenols with monohydric or dihydric alcohol using as germanium oxide as a catalyst, and by adopting such a reaction embodiment, by-production of components having higher boiling points composed of dimers of phenols and derivatives thereof as main components is suppressed, and selectivity of ortho-alkylated phenols increases.
Further, the amount of germanium oxide added as a catalyst maybe small, and the amount of germanium oxide added is preferably from 0.05 to 50% by weight, more preferably from 0.1 to 30% by weight, further preferably from 0.5 to 10% by weight based on phenols of the general formula (1).
In any of the production method [I] and the production method [II] of the present invention, it may be conducted by a batch system or by a flow system, and the batch system is preferable.
In any of the production method [I] and the production method [II] of the present invention, since the reaction mixture after completion of the reaction may sometimes contain unreacted raw materials or by-products or impurities in addition to ortho-alkylated phenols of the general formula (1), the ortho-alkylated phenols of the general formula (1) can be separated and purified to purities required for various uses. The separation and purification methods are not particularly restricted, and methods industrially usually used such as distillation, extraction and the like can be applied.
According to the production method of the present invention, ortho-alkylated phenols can be produced from phenols of the general formula (1) and monohydric or dihydric alcohol, using a relatively small reaction vessel, at high selectivity under conditions in which by-production of components having higher boiling points such as dimers of phenols and derivatives thereof and the like is small. The production methods of the present invention have also characteristics that a reaction is possible even if the amount of a catalyst is small, and that by-production of components having higher boiling points is small particularly in the batch system.
According to the method of the present invention, ortho-alkylated phenols can be produced from phenols and alcohol using a relatively small reaction vessel with high selectivity under conditions in which by-production of components having higher boiling points such as dimers of phenols and derivatives thereof, even if the reaction is conducted by batch system, therefore, the method of the present invention is industrially useful.